Optical disk drives have conventionally been made fit for practical use. Data can be recorded on and read from an optical disk by setting the disk on the main body of an optical disk drive and irradiating the disk with a laser beam from the pickup head of the drive. Optical disk drives can read data by discriminating various types of optical disks such as DVD-RAMs and DVD-Rs. A DVD-RAM has a rewritable area and an embossed area. Different methods of tracking servo control are to be used for the two areas.
An optical disk drive that reads DVD-RAMs calculates an address by calculating the number of tracks from the light reflected by the optical disk during a seek. Even though the seek is made while the address is thus calculated, the address just after the seek is liable to differ from the target value due to the inertia of the pickup head that is created during the seek, the dust on the optical disk, etc. Consequently, if a seek is made for an address near the boundary between the rewritable and embossed areas, the beam spot may stop at the wrong area. In this case, no tracking servo control can be performed because the method of tracking servo control for the wrong area differs from the method of tracking servo control for the right area.
A method for moving the pickup head to a condition under tracking servo control includes trying tracking servo control some more times at the address where no tracking servo control was able to be performed. According to this method, if the control trial enables no tracking servo control, the beam spot is moved a long distance to an address where tracking servo control can be performed reliably, and thereafter tracking servo control is performed again.
JP-2003-109233A discloses an optical disk drive that performs tracking servo control for the two areas of a DVD-RAM by determining whether each of them is the rewritable area. This Japanese document also discloses that the determination is performed by detecting from an RF signal the header signal of a sector existing only in the rewritable area. JP-2004-55125A refers to a method for detecting such a header signal.
The foregoing prior art is such that, if no tracking servo control can be performed just after a seek is made for an address, the pickup head is moved to a condition under tracking servo control after it is moved by trying tracking servo control some times at this address. Accordingly, useless tracking servo control may be tried some times by the wrong method of tracking servo control. This makes it take time to move to the pickup head to a condition under tracking servo control.
JP-2003-109233A is such that it is always determined, regardless of track position, whether each of the two areas is the rewritable area. This may result in needless determination, so that the operating speed of the whole disk drive may be low. As a result, if one or more of the files recorded on the optical disk are skipped, it takes time to move the beam spot to the head of the target picture or sound.